I Know Dino: The Big Dinosaur Podcast

Episode 233 is all about Chungkingosaurus, one of the smallest known stegosaurs.

We also interview Andrew McDonald, curator and an educator at the Western Science Center in Hemet, California. His research focuses on the evolution of dinosaurs in North America during the Cretaceous, and he regular does field work in New Mexico. Since becoming curator, he’s already named two new dinosaurs: Dynamoterror and Invictarx.

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Probably looked similar to Tuojiangosaurus (found in the same formation), though smaller, with a high, narrow skull

Probably had two rows of plates and spikes on its back, possibly arranged in pairs

A model of Chunkingosaurus at the Chongqing Municipal museum has 14 pairs of plates, 2 pairs of tail spikes, and the plates in the middle look like thick spikes (similar to Tuojiangosaurus)

Only one specimen found with a thagomizer (tail spikes), and there were two pairs and they were vertical and stout. May have had a third pair, but it was lost during excavation

Fossils found in 1977

Described in 1983 by Dong Zhiming and others

Type species is Chungkingosaurus jiangbeiensis

Name means “Chungking lizard”

Named for where the fossils were found, in the Jiangbei district of Chungking municipality

Four specimens have been found. Zhiming and others described all four, but named the three additional specimens as specimen, 1, 2, and 3, because there are distinctions between the three, but the specimens are too fragmentary in nature

In 2014, Roman Ulanksy named two of the species as new species, Chunkingosaurus giganticus and Chunkingosaurus magnus. But later Peter Galton and Kenneth Carpenter said they were nomina dubia, and referred them both to Chungkingosaurus jiangbeiensis

Gregory Paul suggested in 2010 that the third specimen was a juvenile of Tuojiangosaurus

Part of Huayangosauridae, a group of basal stegosaurs

May have been prey for theropods such as Yangchuanosaurus

Other dinosaurs that lived in the same time and place included Tuojiangosaurus, and sauropods like Mamenchisaurus

Fun Fact:
A typical theropod is about 3 times as long as it is tall when in a walking/running posture.

Lambe was referencing the nasal arch, which resembled a gryphin (for the name “hooked beak”)

Had a narrow, arching nasal hump, that some have described as like a “Roman nose”

The term “gryposaur” is sometimes used to hadrosaurs with nasal arches

Lived in the Late Cretaceous in North America

Found in Dinosaur Park Formation in Alberta, Canada, Two Medicine Formation in Montana, and Kaiparowits Formation in Utah

Similar to Kritosaurus, and for a while it was thought they were synonyms (long history)

First fossils were collected in 1913 by George Sternberg, from Dinosaur Park Formation in Alberta. Found a skull and partial skeleton

Multiple skulls, some skeletons, and some skin impressions have been found

Lawrence Lambe described Gryposaurus in 1914

A few years before the Gryposaurus find, in 1910, Barnum Brown had found and described a partial skull from New Mexico, and called it Kritosaurusnavajovius

Brown’s specimen did not have a snout, so he restored it based on Anatotian (now Edmontosaurus), which had a flat-head

Lambe described Gryposaurus differently (focused on the nasal crest), and in 1916 the Kritosaurus skull was remade to have the nasal arch. Barnum Brown and Charles Gilmore suggested the two were synonyms

This influenced William Park’s decision to name a nearly complete skeleton found in Dinosaur Park Formation Kritosaurusincurvimanus, instead of Gryposaurusincurvimanus (and he let Gryposaurus notabilis stay as its own genus)

Parks considered Gryposaurus to be a junior synonym of Kritosaurus

Hard to compare Kritosaurusincurvimanus and Gryposaurus notabilis because Kritosaurus incruvimanus is missing part of the front of the skull, so we don’t see the full nasal arch

Kritosaurus is only known from partial remians and seem very similar to Gryposaurus (except it lived a little later than Gryposaurus, based on the slightly younger formation where it was found)

In 1942, Lull and Wright published a monograph on hadrosaurs and said Kritosaurus and Gryposaurus were the same

But in the 1990s some scientists questioned Kritosaurusnavajovius (limited material compared to other hadrosaurs), so some think the two genera are different

Some scientists, such as Jack Horner, have suggested that Hadrosaurus is the same as Gryposaurus and Kritosaurus. This was a common hypothesis in the 1970s and 80s. But in 1990 Jack Horner changed his mind and said Gryposaurus was its own genera. Most scientists now think that Hadrosaurus and Gryposaurus have differences in their upper arms and iliums

Horner described the specimens of a second species, Gryposaurus This based based on two parts of skeleton that was collected in 1916 for AMNH (also there was bonebed material)

Three valid species: Gryposaurusnotabilis, Gryposauruslatidens, Gryposaurusmonumentensis (though could be 4-5, depending on who you ask)

Type species is Gryposaurusnotabilis

Gryposauruslatidens has an informal name, Hadrosauravus, that was used early on (no longer used)

There’s a possible fourth Gryposaurus species, Gryposaurusalsatei, found in the Javelina Formation

Stephanosaurusmarginatus was once considered to be a possible Kritosaurus species (when Kritosaurus and Gryposaurus were considered synonymous), but now it’s considered to be dubious

Jack Horner also created the new combination of Gryposaurusincurvimanus

Gryposaurus has been found in various places including Alberta, Utah, Montana, and possibly Texas, so it had a large geographical range

Gryposaurus lasted for at least 5 million years, which is a lot longer than most other taxon in Hadrosauridae (except Edmontosaurus)

Gryposauruslatidens is from the lower Two Medicine Formation in Montana, and lived about 4 million years before other Gryposaurus species appeared ( notabilis and G. incurvimanus), G. monumentensis is about 1-2 million years younger than G. notabilis and G. incurvimanus

Gryposaurusmounmentensis was named in 2007, by Natural History Museum of Utah paleontologists. Scott Sampson called it the “Arnold Schwarznegger of duck-billed dinosaurs”

Fossils found in Utah, a skull and partial skeleton, were named Gryposaurusmonumentensis (found in Grant Staircase-Escalante National Monument). Had a robust skull

Researchers first found Gryposaurusmonumentensis in 2003

Gryposaurusmonumentensis had thick bones in its skull and limbs

Gryposaurusmonumentensis had big jaws, so it could eat tough planet material

Gryposaurusmonumentensis had 300 teeth in its mouth for eating, but it had lots of replacement teeth, so at any time it may have had more than 800 teeth

Gryposaurus was bipedal and quadrupedal

Ate a variety of plants, and could eat food on the ground and up to 13 ft (4 m) off the ground

Ground its food (similar to chewing)

Cropped vegetation with its beak, and had cheek-like organ to keep food in its mouth

As Gryposaurus grew, its nasal arch got bigger

The arch was over an enlarged nasal opening, which may have held soft tissue

Nasal arch was probably covered by thick, keratinized skin, or had a cartilaginous extension

Nasal arch may have been for fighting each other, or for species or sexual dimorphism

Nasal arch may also have been used to help push or butt in contests, and it may have had inflatable air sacs (visual and audio signals)

About 30 ft (9 m) long, though one species

Had scales along the midline of its back

Had pyramidal and ridged scales

Saurolophine hadrosaurid (subfamily with hollow crests on their heads)

Gryposaurus was for a while considered to be a hadrosaurine, but then Hadrosaurus was found to be different from other dinosaurs classified as hadrosaurines. Then Hadrosaurus was given a place beneath Hadrosauridae, but hadrosaurinae could no longer be used because it didn’t include Hadrosaurus. So the next oldest genus in that group, Saurolophus, becuase the type genus of Saurolophinae, and now Gryposaurus is considered to be a saurolophine

Probably lived on a floodplain with swamps, ponds, lakes, in a wet and humid climate

May have preferred being by the river

Other dinosaurs that lived in the same time and place include Centrosaurus and Corythosaurus, dromaeosaurids, troodontids, ornithomimids, ankylosaurids, tyrannosaurids (Albertosaurus and Teratophoneus), Parasaurolophus, ceratopsians such as Utahceratops and Nasutoceratops, and oviraptorosaurians such as Hagryphus

Also lived among sharks and rays, frogs, salamanders, turtles, lizards, crocodilians, and early mammals (marsupials and insectivorans)

Where Gryposaurus lived was a relatively small area, and there were other hadrosaur species around at the same time and place. Yet, they didn’t seem to intermingle, and it’s unclear why (since there were no known physical barriers, like mountains, to get in their way). It’s also not clear how such a relatively small area support so many large herbivores. One hypothesis is that hadrosaurs and other large herbivores had slower metabolisms, or maybe there were a large amounts of plants to eat, or the climate in the area, known as “West America” varied across latitudes, so plants in different areas would have been different, and that’s why dinosaurs may not have mixed

Fun Fact:

Japan was connected to the rest of Laurasia for the entire Mesozoic, so dinosaurs could come and go freely

Brief history summarized from Origins of the Japanese Islands: The New “BigPicture” By Gina L Barnes Published in Japan Review: